Printed circuits widely used in electronics and electrical devices, are formed with major dimensions of length and width and contain one or more circuits. The thickness of the printed circuit panels varies for many different reasons and directly affects panel flexibility, i.e., there are rigid and flexible circuit boards.
For example, printed circuits with multiple conductor planes use a bonded dielectric layer or layers for separation. Holes perforated through the circuit substrate serve a number of purposes including solder terminals for installation into another assembly, plated through hole interconnections between conductor planes and tooling registration holes.
Exposed copper on the finished printed circuit panels must, with few exceptions, be solder coated, a process sometimes termed presoldering or soldering. It is preferable that the solder coating be applied only where needed later and not on all conductor runs. To apply solder selectively, a dielectric, referred to as a cover dielectric or solder mask, is used to cover copper, the normally used conductor, that need not be solder coated. Thus desired copper portions remain exposed and are solder coated, including terminal pads and the like. In other words, the exposed copper on the surface or surfaces of the printed circuit must be effectively solder coated.
It is also necessary that all holes through the printed circuit be lined with solder but unobstructed by solder when finished, so as not to obstruct later component lead insertion requirements. The process of removing excess surface solder and clearing the holes of solder, after solder coating the surface conductors, is referred to as solder leveling or leveling
In other words, printed circuit panels are soldered, inter alia, to maintain solderability for subsequent operations. For economic purposes, such soldering should be accomplished as a mass panel coating technique and should provide even coatings on the surfaces and in holes without surface flaws.
An apparatus for soldering printed circuit panels is disclosed in my U.S. Pat. No. 4,608,941 for "Apparatus for Soldering Printed Circuit Panels". My prior patented apparatus includes a roll configuration to convey the panels horizontally across a solder immersion station containing a flow of molten solder. Immersion of the circuit panels in flowing solder is followed by subjecting the panels to suitably positioned air knives for leveling the solder on the panels.
An improvement in the apparatus of my U.S. Pat. No. 4,608,941 is disclosed in my copending application Ser. No. 199604 filed May 31, 1988, now U.S. Pat. No. 4,903,631. According to my aforesaid application Ser. No. 199604, the solder immersion station is defined by upper and lower retainer guide means and two pairs of rolls. Each roll pair includes an upper roll and a lower roll, the rolls functioning to convey printed circuit panels horizontally through the chamber. The guide means are parallel to the rolls and the lower guide means is positioned close to the lower rolls to minimize solder leakage. The solder immersion stations also includes means adjacent the ends of the pairs of rolls for further enclosing the solder chamber. An opening is provided in the lower guide means parallel to the rolls for communication with a manifold positioned parallel to end below the solder chamber. Means are provided for pumping solder into the manifold to flood the solder chamber through the opening. Vertical manifolds close the ends of the immersion chamber and provide an additional vertical flow path to carry solder up and around panels passing through the chamber to ensure a full solder chamber. The lower guide includes lips positioned closely to the surface of the lower rolls to prevent excessive leakage of solder from the chamber before and as the rolls convey the panels through the molten solder.